Relationship Between the Ability to Detect Frequency Changes or Temporal Gaps and Speech Perception Performance in Post-lingual Cochlear Implant Users.

Purpose: Acoustic change complex (ACC) reflects brain’s capacity to discriminate the acoustic features present in the signal, hence serves as an index of discrimination capacity. ACC for intensity changes and gaps-in-noise have consistently shown that the ACC threshold is consistent with behavioral intensity discrimination and gap detection thresholds. While, the ACC threshold for frequency change is found to be highly variable. The present study was carried out to investigate the agreement between behavioral frequency discrimination threshold and the ACC threshold for frequency change.Methods: Ten young adults with normal hearing in both ears participated in the study. The ACC was elicited using frequency changing tones, with a frequency change of 5, 10, 25, 50, 100 and 200 Hz.Results: The present study showed that a greater frequency change is required to elicit the ACC compared to behavioral discrimination threshold. In most of the participants, a frequency change greater than 50 Hz was required to elicit the ACC. Magnitude of frequency change had effect on latency and amplitude of peaks of the ACC, amplitude was higher and latency was shorter for greater frequency change.Conclusion: ACC threshold for frequency change does not resemble behavioral discrimination threshold and is variable across participants.

Objective:This paper reports a noninvasive method for quantifying neural synchrony in the cochlear nerve (i.e., peripheral neural synchrony) in cochlear implant (CI) users, which allows for evaluating this physiological phenomenon in human CI users for the first time in the literature. In addition, this study assessed how peripheral neural synchrony was correlated with temporal resolution acuity and speech perception outcomes measured in quiet and in noise in post-lingually deafened adult CI users. It tested the hypothesis that peripheral neural synchrony was an important factor for temporal resolution acuity and speech perception outcomes in noise in post-lingually deafened adult CI users.Design:Study participants included 24 post-lingually deafened adult CI users with a Cochlear™ Nucleus® device. Three study participants were implanted bilaterally, and each ear was tested separately. For each of the 27 implanted ears tested in this study, 400 sweeps of the electrically evoked compound action potential (eCAP) were measured at four electrode locations across the electrode array. Peripheral neural synchrony was quantified at each electrode location using the phase locking value (PLV), which is a measure of trial-by-trial phase coherence among eCAP sweeps/trials. Temporal resolution acuity was evaluated by measuring the within-channel gap detection threshold (GDT) using a three-alternative, forced-choice procedure in a subgroup of 20 participants (23 implanted ears). For each ear tested in these participants, GDTs were measured at two electrode locations with a large difference in PLVs. For 26 implanted ears tested in 23 participants, speech perception performance was evaluated using Consonant-Nucleus-Consonant (CNC) word lists presented in quiet and in noise at signal-to-noise ratios (SNRs) of +10 and +5 dB. Linear Mixed effect Models were used to evaluate the effect of electrode location on the PLV and the effect of the PLV on GDT after controlling for the stimulation level effects. Pearson product-moment correlation tests were used to assess the correlations between PLVs, CNC word scores measured in different conditions, and the degree of noise effect on CNC word scores.Results:There was a significant effect of electrode location on the PLV after controlling for the effect of stimulation level. There was a significant effect of the PLV on GDT after controlling for the effects of stimulation level, where higher PLVs (greater synchrony) led to lower GDTs (better temporal resolution acuity). PLVs were not significantly correlated with CNC word scores measured in any listening condition or the effect of competing background noise presented at a SNR of +10 dB on CNC word scores. In contrast, there was a significant negative correlation between the PLV and the degree of noise effect on CNC word scores for a competing background noise presented at a SNR of +5 dB, where higher PLVs (greater synchrony) correlated with smaller noise effects on CNC word scores.Conclusions:This newly developed method can be used to assess peripheral neural synchrony in CI users, a physiological phenomenon that has not been systematically evaluated in electrical hearing. Poorer peripheral neural synchrony leads to lower temporal resolution acuity and is correlated with a larger detrimental effect of competing background noise presented at a SNR of 5 dB on speech perception performance in post-lingually deafened adult CI users.

Temporal gap detection was measured as a function of absolute signal bandwidth at a low-, a mid-, and a high-frequency region in six listeners with normal hearing sensitivity. Gap detection threshold decreased monotonically with increasing stimulus bandwidth at each of the three frequency regions. Given conditions of equivalent absolute bandwidth, gap detection thresholds were not significantly different for upper cutoff frequencies ranging from 600 to 4400 Hz. A second experiment investigated gap detection thresholds at two pressure-spectrum levels, conditions typically resulting in substantially different estimates of frequency selectivity. Estimates of frequency selectivity were collected at the two levels using a notched-noise masker technique. The gap threshold-signal bandwidth functions were almost identical at pressure-spectrum levels of 70 dB and 40 dB for the two subjects in experiment II, while estimates of frequency selectivity showed poorer frequency selectivity at the 70-dB level than at 40 dB. Data from both experiments indicated that gap detection in bandlimited noise was inversely related to signal bandwidth and that gap detection did not vary significantly with changes in signal frequency over the range of 600 to 4400 Hz. Over the range of frequencies investigated, the results indicated no clear relation between gap detection for noise stimuli and peripheral auditory filtering.

Background Cochlear implants (CI) can partially or totally revert the effects of sensory deprivation; thus enabling the development of auditory abilities. However, there remains a large amount of variability in speech perception outcome among CI users. Such variability may be attributed to the children’s diverse capabilities in detecting amplitude, temporal and spectral changes in the incoming complex speech signals in quiet and in difficult listening situations. Objective To study whether the newly introduced Acoustic Change Complex (ACC) cortical potential using short duration can be used to document such variability. If used as a tool for cortical discrimination, it will aid in evaluating young children who cannot be tested using behavioral measures. Patients and Methods Cortical auditory evoked potentials were recorded in forty five unilaterally-implanted children ranging in age from 6 to 12 years. Stimuli used to elicit ACC were short duration (500 msec.) speech and tonal stimuli. Spectral change was done using /i/ to /u/ vowels, while temporal change was done using variable gaps-in-1000 Hz tone, ranging from 5 msec. to 200 msec. Auditory evoked responses were compared to behavioral tests which included speech perception test (PBKG) and psychophysical test for temporal resolution. Results ACC potentials were successfully recorded in most of the children evaluated. Generally, ACC were significantly highly detected in temporal changes than spectral change. Individual data showed that poor behavioral performance was associated with higher ACC detection thresholds to gap in tone and poorer % detection to vowel change. Conclusion: ACC potential using short duration stimuli can be recorded in young implanted children in an ordinary clinical setting. However, more research is needed to document the complex behavioral-objective relationship and its ultimate link to speech perception and language development in young CI recipients.

Temporal gap detection thresholds were measured in narrow-band noise-burst markers having acoustic characteristics representative of isolated steady-state second-formant (F2) properties for/p,t,k/paired separately with/i,ae,u,o/. The results revealed that gap detection threshold increased systematically as the difference was increased between the simulated stop and vowel F2 frequencies. A strong positive correlation (r = 0.87) between gap detection threshold and linear marker center frequency difference was highly significant (p < 0.001). Differences in other stimulus features had little influence on gap detection performance. Implications for speech perception are discussed.

Objective: Assess whether differences in speech perception are observed after exclusive listening experience with high-definition continuous interleaved sampling (HDCIS) versus fine structure processing (FSP) coding strategies.Methods: Subjects were randomly assigned at initial activation of the external speech processor to receive the HDCIS or FSP coding strategy. Frequency filter assignments were consistent across subjects. The speech perception test battery included CNC words in quiet, HINT sentences in quiet and steady noise (+10 dB SNR), AzBio sentences in quiet and a 10-talker babble (+10 dB SNR), and BKB-SIN. Assessment intervals included 1, 3, and 6 months post-activation.Results: Data from 22 subjects (11 with HDCIS and 11 with FSP) were assessed over time. Speech perception performance was not significantly different between groups.Discussion: Speech perception performance was not significantly different after 6 months of listening experience with the HDCIS or FSP coding strategy.

Assessment of outcome measures after audiological computer-based auditory training in cochlear implant children

This study aims to objectively evaluate temporal processing capabilities using the electrically evoked auditory change complex (eACC) in patients with auditory brainstem implants (ABIs). Study participants include seven Cochlear Nucleus 24M ABI recipients (six children and one adult). All children received ABIs due to cochlear nerve deficiency and the adult recipient was diagnosed with neurofibromatosis type II (NF-2). The speech processor was bypassed and electrical stimulus was a biphasic pulse train directly sent through individual electrodes of the ABI. Gap durations tested in this study ranged from 4 to 256 ms. Amplitude modulation frequency was 10 Hz. Modulation depths tested in this study ranged from 1% to 99%. Behavioral gap detection thresholds were also obtained for two participants. The eACCs were evoked by temporal gaps and amplitude modulations. The shortest gap duration and the smallest amplitude modulation depth that can be used to evoke the eACC vary across study participants and across stimulating electrodes within individual participants. These preliminary data also suggest that the temporal gap detection primarily depends on subcortical auditory neural structures. The eACC can be used to objectively evaluate temporal processing capabilities in both adult and pediatric ABI recipients.

The goal of this paper is to show the impact of the tracer size and the temporal gap between images in atmospheric motion vector (AMV) extraction schemes. A test has been performed using NWC SAF/High Resolutions Winds AMV software for different configurations with a tracer size varying between 8 × 8 and 40 × 40 pixels and a temporal gap between images varying between 5 and 90 min. AMVs have been extracted for four different MSG/SEVIRI channels (HRVIS, VIS0.8, WV6.2, and IR10.8) over the European and Mediterranean area for a 6-month period (January–June 2010). The AMV performances have been tested against radiosonde winds and ECMWF model analysis winds. The results show a small impact of the tracer size on the number of valid AMVs, which is, however, more significant for clear air AMVs, and a significant impact of the temporal gap between images. The largest number of valid AMVs has been found in general for a temporal gap of 5 min for the 1-km pixel scale and for a temporal gap of 10 min for the 3-km pixel scale. Results also show a decrease of the mean AMV speed and the normalized BIAS (NBIAS) with larger tracer sizes, and a relatively small impact of the temporal gap on these parameters. Finally, the results show minimum values of the normalized root-mean-square vector difference (NRMSVD) for intermediate temporal gaps between 15 and 30 min with a relatively small impact of the tracer size on this parameter.

Formby and Forrest [J. Acoust. Soc. Am. 89, 830–837 (1991)] measured temporal gap detection (TGD) thresholds as function of frequency separation between two sinusoids marking a silent temporal gap. Their results were fit well with a roex-filter model. Filter estimates (1) were based on TGD thresholds for post-gap marker frequencies F2≥ pre-gap marker frequencies F1 and (2) assumed symmetry of the roex-filter function for F2≤F1. In a related study, TGD thresholds were measured with narrow-band markers [Formby etal., J. Acoust. Soc. Am. 93, 1023–1027 (1993)]. The resulting thresholds raised doubts about the earlier assumption of filter symmetry. To resolve this issue, TGD thresholds were measured for F2 frequencies presented above and below F1=500 and 4000 Hz for a range of marker and masker presentation levels. Roex functions fitted for conditions of F2≥F1 were typically shallower than those fitted for conditions of F2≤F1. The same qualitative patterns of filter asymmetry have also been found and will be reported for TGD thresholds simulated by single- and multi-channel auditory models [Forrest and Formby; Heinz etal., companion papers at this meeting]. [Research supported by NIH.]

Breaking News

A cochlear implant (CI) is a hearing device introduced in the 1980s for profoundly deaf subjects who gained little or no benefit from powerful hearing aids. This device comprises an electrode array inserted in the cochlea, connected to an internal receiver, and an externally worn speech processor. The CI transforms acoustic signals into electrical currents which directly stimulate the auditory nerve. Since the early 1990s, cochlear implantation in children has been developing rapidly. Although it is still difficult to predict how a child will perform with a cochlear implant, the success of cochlear implantation can no longer be denied. In this paper, some recent papers and reports, and the results of the various Nijmegen cochlear implant studies, are reviewed. Issues about selection, examinations, surgery and the outcome are discussed. Overall, our results were comparable with those of other authors. It can be concluded that cochlear implantation is an effective treatment for postlingually deaf as well as prelingually (congenital or acquired) deaf children with profound bilateral sensorineural deafness.

Previous studies demonstrated prolonged development of degraded speech perception, perhaps due to the maturation of auditory and cognitive brain regions. We investigated the contributions of auditory cortical encoding, measured by the acoustic change complex (ACC), and cognition to speech perception in adolescents (10–17) and young adults (18–23). Speech conditions included the QuickSIN and perception of 6-band noise-vocoded sentences, followed either by silence or multitalker babble. The ACC was measured to a frequency change condition (1000–950 Hz) and gap detection condition (10 ms gap in noise). Cognitive testing was also administered. Separate hierarchical stepwise regressions were completed for each condition. Preliminary results suggest that testing order (silence or babble first) exclusively affected performance on the NV silence condition. Encoding of timing information (ACC for gaps) contributed to the NV silence condition only, whereas encoding of spectral information (ACC for frequency) contributed to both NV speech conditions. Strategy use and sustained attention contributed to both NV speech conditions but age did not explain any unique variance after all factors were included. For the QuickSIN, auditory working memory and vocabulary contributed to performance, and age continued to influence performance after accounting for all other factors. [Funded by NIDCD.]

Experiments with the Rashbass ‘step-ramp’ paradigm have revealed that the initial catchup saccade that occurs near pursuit onset uses target velocity as well as position information in its programming. Information about both position and motion also influences smooth pursuit. To investigate the timing of velocity sampling near the initiation of saccades and smooth pursuit, we analyzed the eye movements made in nine ‘step-ramp’ conditions, produced by combining –2, 0 and +2 deg steps with –8, 0 and +8 deg/s ramps. Each trial had either no temporal gap or a 50-ms gap during which the laser target was extinguished, beginning 25, 50, 75 or 100 ms after the step. Six subjects repeated each of the resulting 45 conditions 25 times. With no temporal gap, saccades were larger in the step-ramp-away’ than the ‘step-only’ condition, confirming that saccade programming incorporates ramp velocity information. A temporal gap had no effect on the accuracy of saccades on ‘step-only’ trials, but often caused undershoots in ‘step-ramp’ trials. A 50-ms gap within the first 100 ms also increased the latency of the initial saccade. Although initial pursuit velocity was unaffected by a temporal gap, a gap that started at 25 ms reliably delayed pursuit onset for ramp motion of the target toward the fovea. Later gaps had a minimal effect on initial pursuit latency. The similar timing of the temporal gaps in target motion information that affect the initiation of saccades and pursuit provides further behavioral evidence that the two types of eye movements share pre-motor neural mechanisms.

The ability of subjects to detect temporal gaps between bursts of sinusoids or bursts of bandlimited noise was measured to evaluate the phenomenon of tactile "sensory persistence" in older persons. Vibratory stimuli were delivered to the right thenar eminence of 27 subjects ranging in age from 8-75 years. The subjects' task was to detect the presence of a silent interval or "gap" between flanking 350-ms vibrotactile stimuli. The gap-detection threshold, expressed as the amplitude of vibration relative to the absolute detection threshold, decreased as the gap duration increased and was higher for gaps in noise than for gaps in sinusoids. The threshold for detecting short gaps increased with age for noise stimuli, but not for sinusoidal stimuli. Furthermore, the gap-detection threshold recovered more rapidly in older subjects for noise stimuli, but less rapidly in older subjects for sinusoidal stimuli. Because of these differences, it appears that the effects of age on gap detection cannot be due to a simple increase in sensory persistence, but may be due to multiple processes.